1. Field of the Invention
The present invention relates to a propulsion system for a boat, and more particularly relates to a propulsion system for a boat equipped with an engine.
2. Description of the Related Art
Conventionally, a propulsion unit for a boat equipped with an engine (a propulsion system for a boat) has been known (see Patent publication JP-A-Hei 9-263294, for example). Patent publication JP-A-Hei 9-263294 discloses a propulsion unit for a boat equipped with an engine and a power transmission mechanism for transmitting a driving force of the engine to a propeller at a given, fixed gear reduction ratio. This propulsion unit is constructed such that the driving force of the engine is directly transmitted to the propeller through the power transmission mechanism and such that the rotational speed of the propeller increases as the engine speed increases.
However, in the propulsion unit (propulsion system) disclosed in the JP-A-Hei 9-263294, it is difficult to improve acceleration performance at low speed if the gear reduction ratio of the power transmission mechanism is arranged to increase the maximum speed. On the contrary, if the gear reduction ratio of the power transmission mechanism is arranged to improve the acceleration performance at low speed, it is difficult to increase the maximum speed. That is, in the propulsion unit for a boat disclosed in the JP-A-Hei 9-263294, it is difficult to achieve both the acceleration and maximum speed at performance levels that an operator of a boat desires.